The labeling and marking of material and products is becoming of rising importance in many industrial fields. The labels and marks are predominantly generated using conventional techniques such as printing, stamping, engraving or embossing. Marking via the application of laser radiation has been established as interesting alternative to these techniques since it is rapid, can be applied on non-planar surfaces and is in general durable and abrasion-resistant due to the inscription in the material, in particular plastic material, itself.
Laser marking methods have been described for different materials, in particular for plastics or polymeric materials. The underlying effect is generally based on an interaction between the polymeric matrix of the material or a laser sensitive additive to said material with a laser beam, which generates a high degree of thermal energy at the laser target point. The application of energy is assumed to result in pyrolysis, carbonization and/or ablation of material, leading to macroscopic modifications of the material, which are optically detectable for the human eye. U.S. Pat. No. 6,284,184 discloses a method of laser marking a plastic substrate based on a layered polymeric substrate, which is ablated in order to reveal a differently colored layer underneath. U.S. Pat. No. 4,822,973 discloses a system, in which the laser radiation passes through the surface of a first layer material and becomes absorbed in a second layer material leading to a laser conveyed marking therein.
The described methods are focused on the generation of generally visible labels or modifications on the treated material, which may however not be applicable in situations in which an optical reaction other than optical reflection is required.
There is thus a need for techniques and materials which overcome the shortcomings of the prior art.